At what point do you ditch factory wiring?

[HankScorpio]

I am installing ProFlo4 in my '91 K5. I also plan on aftermarket gauges, I have swapped to a 454. Everything in my harness was working, ate a crank bearing and pulled out the TBI 350. Thinking of a custom dash to clear a roll cage.
At what point do you start fresh on wiring?
Should I just keep the factory gauges?
I don't see any advantage to ditching the lights and column functions, but how interconnected is the wire harness? Without the need for the factory computer to read sensors there is a ton of wiring left unused. I would like to leave whatever I can, "might as well" projects go on forever, I miss driving my K5.

Guys who have headed down this road, what did you do and what should you have done? Feel free to wander with your thoughts, I will put my actual process into my K5 build thread. Looking for opinions and regrets from your squarebody wiring experiences. I prefer uncut factory wiring but I am moving to a point where this is likely no longer possible. Cutting up a factory TBI harness makes me sad, help me think I am doing the right thing.

 

[Babaganoosh]

For me it was when I needed more and to many butt joints and other ways to make it work.

I wanted a fresh clean platform to work off of and don't regret it at all.

 

[toomany]

I put an EZ-Wiring harness in my 86. I was starting from a bare cab, doing an LS swap, fuel injection, new gauges, better lighting, aftermarket AC, remote start, PW/PL, etc... For me it was just easier to toss out the factory stuff and start fresh. Add in the fact I was missing a few portions of the factory harness and it was a no brainer.

There are a bunch of different manufactures of aftermarket wiring. Some cost way more than they should (looking at you Painless). Ez-Wiring and American Auto Wire are two of the others that are more budget friendly. Most are based on GM wiring colors and fuse boxes. My kit (18 circuit I believe) came with everything to plug into a GM column and headlight switch. Had decent directions as well.

Best way to go about an entire rewire is to plan out every circuit, wire colors and route for each one. Grouping like sections together. Making it easily serviceable, I added Weather Pack connectors in a few of the runs. It's not difficult, just take a little pre planning and thought.

 

[ryoken]

i often base my custom systems off the standard GM ignition switches at the base of the column... repin the vehicle side as needed... key switch, and whatever column accs you choose... I'm a fan of early "turn only" columns.. and the rest of the rig can be custom, or a blend... next decision is circuit protection style.. factory style fuse setup like a painless, etc..., aftermarket like a Ron Francis say.. or full custom fuse or breaker setup like my marine schtuff...

 

[nvrenuf]

@HankScorpio check my build thread. I reached the point with my 91 where I no longer needed 90% of the wiring in the dash (also no factory gauges) and when I tried to trim the harness down I found that quite a bit was interconnected. My solution was a custom plug & play harness with fuse box that only feeds the column switches, headlight switch and a few requested accessory wires.

I did not know about American Autowire until afterwards but I did find that Painless Wiring stuff is unfinished and it’s not customizable with respect to deleting unnecessary circuits. IMO, Painless is too expensive for what they won’t do and you still have to put together yourself. I paid a Facebook vendor literally half of what Painless wanted plus the harness was complete to the connectors and customized to my list of wants and deletes.

 

[nvrenuf]

I start rambling about wiring here - https://ck5.com/forums/threads/91-k...harness-no-more-rats-nest.217030/post-4092276

 

[ZooMad75]

So in my mind, it really comes down to how hacked up your existing wiring is. Also, it's important to note all the wiring for the OEM gauges is independent of the stock TBI wiring. So you don't technically have to use aftermarket gauges if you don't need to.

When we originally put the 5.3 in my '91 we eliminated all the TBI wiring. I kept the vss wiring to the DRAC module and also deleted the ABS. The 5.3 needed a coolant temp sensor which I used the stock one that would have came with the 5.3. Stock TBI oil pressure sensor screwed right in. I had a co-worker turn down a stock TBI coolant temp sensor to fit the metric opening on the opposite head and ran the stock coolant gauge wire to it. So the stock gauges worked just fine with the LS swap. All we had to do with the change to the 8.1 was going back to a stock TBI coolant sensor to go into the head vs the modified one I used in the 5.3. It works just fine with the 8.1.

Thankfully in my case, only the TBI wiring was really hacked on my truck. It really didn't push any need to rewire.

If you want to ditch the factory dash for something that will clear a roll cage it would make ditching the factory wiring easier for sure.

 

[6872xtc]

When I put the proflo in my '90, I did the same as Rob and trimmed out the TBI wiring. I hated to do it, same as you, but I didn't want a mess hanging out under the hood. I still haven't finished up at the bulkhead connector though.
I did find that there were a couple of wires that ran with the TBI harness which need to stay. I think that it was for the speedometer, I can't remember exactly.

So if you are going with custom dash and gauges, you may be better off going with new harness if the speedometer doesn't use the DRAC module. If you don't have power windows and locks, then there is less to integrate into with a new harness.
Maybe you can save the whole factory harness for a different truck or someone. I have one in a plastic tub, don't know if it will ever get used though.

 

[HankScorpio]

When I put the proflo in my '90, I did the same as Rob and trimmed out the TBI wiring. I hated to do it, same as you, but I didn't want a mess hanging out under the hood. I still haven't finished up at the bulkhead connector though.
I did find that there were a couple of wires that ran with the TBI harness which need to stay. I think that it was for the speedometer, I can't remember exactly.

So if you are going with custom dash and gauges, you may be better off going with new harness if the speedometer doesn't use the DRAC module. If you don't have power windows and locks, then there is less to integrate into with a new harness.
Maybe you can save the whole factory harness for a different truck or someone. I have one in a plastic tub, don't know if it will ever get used though.

I have been reading through your setup in the proflo thread, its looking like what I will do. Mines a '90 also. Hook up what I need and trim out the rest. Not afraid to wire the K5 from scratch but it is a ton of work that isn't really needed. I don't see myself ever going back to the TBI. I used the 454 because I had it, its a rebuilt 0 mile unit, and its got an old school cool factor. If I go a different route some day it will probably be an LS. If I hadn't already had the rebuilt 454 an LS would have been my choice. Not to jump on the bandwagon, they just make so much power and don't leak much. The proflo for LS engines looks interesting too, could be a cool setup for the same reasons, LS engine management in 1 box with customer service hotline.

 

[1-ton]

With my 1991 V3500 crew cab I just ran all new wiring in the engine bay while the engine was out of it. Since there is no such thing as a wire-harness kit for my truck I just replaced all the wiring one wire at a time. I ran all new wiring from the ECM wiring grommet on the fire wall, and from the junction block on the firewall. My crew cab came with a 4L80E trans that has speed sensors and internal wiring harness that are controled by an ECM/PCM. This negated the abillty to do any midification to the stock TBI harness.

 

[HankScorpio]

With my 1991 V3500 crew cab I just ran all new wiring in the engine bay while the engine was out of it. Since there is no such thing as a wire-harness kit for my truck I just replaced all the wiring one wire at a time. I ran all new wiring from the ECM wiring grommet on the fire wall, and from the junction block on the firewall. My crew cab came with a 4L80E trans that has speed sensors and internal wiring harness that are controled by an ECM/PCM. This negated the abillty to do any midification to the stock TBI harness.

My 1991 V3500 crew cab is the manual. It has the VSS in the 205 but no cruise control so less wiring than your 4L80 setup. My 1990 K5 has the electronic VSS, it came with a 241. When I swapped it to SM465/NP205 I did the tail shaft housing mod for electronic VSS. Got the speedometer working and the check engine light went away. These are some of the interconnected things I wonder about. If I pull out the factory computer will the check engine light come on? Will the speedometer still work? I think the speedometer will work fine without the computer but the VSS feeds both somehow.

 

[frankin5]

The VSS feeds the DRAC ( little white module under dash below radio) on the 91. Goes to DRAC , which sends the signal to speedometer and to the computer.

 

[ZooMad75]

My 1991 V3500 crew cab is the manual. It has the VSS in the 205 but no cruise control so less wiring than your 4L80 setup. My 1990 K5 has the electronic VSS, it came with a 241. When I swapped it to SM465/NP205 I did the tail shaft housing mod for electronic VSS. Got the speedometer working and the check engine light went away. These are some of the interconnected things I wonder about. If I pull out the factory computer will the check engine light come on? Will the speedometer still work? I think the speedometer will work fine without the computer but the VSS feeds both somehow.

So unlike later systems, the vss signal is not direct to the ecm. It's actually pretty simple with the DRAC module. The signal goes from the VSS to the the DRAC and from there the DRAC sends the signal to the cluster, cruise module, and abs module. The nice thing is the signal is on individual circuits to each of those so if you delete the factory ecm and abs like I did, the cluster still works.

If I remember right the ecm commands the ground for the check engine light so with the factory ecm out of the way there isn't anything to command the ground so it won't work.